There may have been pigeons and gulls rather than dragons and owls wheeling across the moody skies over Trafalgar Square early on Thursday, but to the faithful, who clutched umbrellas and wands in roughly equal ratio, neither the birds nor the weather were of the slightest consequence.

They had not come to ride Nelson's lions or run the gauntlet of the English summer: they had come from across the world to pay their final respects to a young, bespectacled wizard whose adventures began before many of them were born.

It was not hard to distinguish the Harry Potter acolytes from the commuters and civil service muggles trudging grimly towards Whitehall.

By 7am, the fans – if the word is strong enough – were dragging their aching bodies into nearby coffee shops, many still clutching the pillows that had made the previous few nights of bunking down in Trafalgar Square marginally more comfortable.

Around their necks were red and gold striped scarves and on their foreheads, predominantly in black marker, was a small lightning bolt and, in one case, a three-initial salute to the wizard's beloved creator: JKR.

Despite being herded into pens that might have served as kettles under different circumstances, the mood was almost bewitchingly buoyant.

Lauren Hill, who had travelled from Vancouver with her friends Sam and Scottie, felt virtually any sacrifice would be worth enduring if it meant she could be in London for the premiere of Harry Potter and the Deathly Hallows – Part 2.

"I wanted to be the first person here for my love of Harry Potter," said the 20-year-old. "It's the final one. I had to come."

But did the prospect of catching a glimpse of Jo Rowling and Daniel Radcliffe really justify five days of sleeping rough in central London?

"I'm running on fumes now because I haven't slept for the last three nights," she said. "But it'll be worth it 100%. And I'd do it all again – in the snow."

Sam and Scottie nodded approvingly.

The square, which had the slightly naughty atmosphere of an adolescent festival, was thick with such devotion.

Safely beyond the reach of the real and parental worlds, gaggles of teenagers felt free to worship at the altar of Potter – and enjoy the first fruits of independence.

Some tucked into an 8am breakfast of prawn cocktail crisps, while others began unfurling banners and placards, ranging from the witty ("Keep calm and carry a wand") to the satirical ("Is this the queue for the Justin Bieber Tickets?") and even the risque: ("I'd be easy 4 a Weasley").

Oliver, a 14-year-old from Helsingborg in Sweden who had persuaded his parents to let him stay in the square while they wisely slept in a hotel, was in a reflective mood as he stood behind a barrier and pondered what the day meant.

"I've grown up with the stories and this is the last chance I'll have to do this properly," he said.

"It's a way of saying goodbye to a part of your life. It's really exciting to be seeing the movie, but I don't want it to stop."

His parents need not have worried. Apart from the treacherous weather and a ban on putting up tents, the worst that the Trafalgar Square sleepers had to suffer was the occasional inquisition at the hands of over-refreshed Londoners wanting to know what on earth they thought they were doing.

"Never in my wildest dreams did I think I would be in the front row," mused Oliver. "I still can't believe this is happening."

Across the red carpet that would later lead Rowling and the cast all the way to Leicester Square, Sabrina Altnann, a 23-year-old housewife from near Cologne, was also feeling a touch overwhelmed.

"I'm a little bit sad that it's the last movie, but it's a great event and it's something that we'll never have the chance to do again," she said.

Around her, as huge banners showing a defiant Harry and a terrifying Lord Voldemort flapped in the wind, the young crowd discussed who they were most excited about seeing later on: Daniel or Jo? They appeared almost evenly split, although the gratitude and affection they had for the author may just have outstripped their love and lust for the actor.

"I want to meet Jo Rowling to thank her for her words and her inspiration," said Richard Bennett, a 35-year-old writer from Southend. "It's the end of an era."

That thought – and the realisation that, for many, the conclusion of the saga also heralded the end of an innocence that many muggles simply cannot comprehend – hung over the faithful as heavily as the rain clouds. But, then, as Sabrina pointed out, there was no reason why the spell shouldn't remain unbroken. "Harry Potter will never leave," she said. "He will always be here. He is our childhood."